Early, gentle input may make lane departure prevention more accepted

Guiding drivers to stay in their lanes with slight nudges from the steering wheel and subtle braking as soon as tires start to drift versus later and more abrupt interventions may be key to boosting use of lane departure prevention systems, a new IIHS study indicates.

Of all current crash avoidance technologies, features meant to help drivers stay in their travel lane get turned off the most. Still, some lane departure prevention systems manage to escape driver scorn.

A 2017 IIHS observational survey of vehicles brought to dealership service centers found that lane departure prevention systems in General Motors and Volvo vehicles were more likely to be active than ones in Ford and Honda models (see "Lane maintenance systems still a turnoff for many drivers," June 22, 2017). All of the systems are designed to keep vehicles in their lanes by warning, braking, and/or steering, and drivers can deactivate them.

In new on-road tests, IIHS researchers dug into the characteristics of lane departure prevention systems from Ford, General Motors, Honda and Volvo to evaluate where steering or braking occurred relative to lane markings, and whether the efforts successfully kept the vehicles in their travel lanes.

The specific functions of each system vary slightly, but all are designed to help avoid crashes due to unintended lane departures, which can occur when drivers are distracted or drowsy. If sensors detect the vehicle approaching a lane marking when the turn signal isn't activated, the system acts to redirect the vehicle with automated steering or braking. Each system also may try to get the driver's attention with auditory, visual, or tactile warnings.

IIHS technicians outfitted all of the vehicles with two exterior and two interior cameras, plus a data logger with a GPS antenna to record vehicle speed, latitude and longitude. Yaw rate also was recorded. Tests were conducted at 50 mph with cruise control engaged on a four-lane divided road.

In each vehicle, a test driver induced 40 lane drifts on left and right curves by steering the vehicle straight into the curve so that vehicles departed in the opposite direction and 40 lane drifts on straightaways by slight steering input to direct the vehicle to the left and right lane markers.

Researchers used video from the outboard cameras and video from the camera aimed at the steering wheel to assess whether a vehicle crossed lane markers by more than 35 centimeters (about 14 inches) on any of its trials.

Both the Malibu and S90 systems provided steering input further inside the lane than the Accord and Fusion, and they produced the lowest mean peak changes in the yaw rate. On both curves and straightaways, the Malibu and S90 avoided a much larger proportion of lane marker crossings exceeding 35 centimeters than the Accord and Fusion.

The Volvo S90's lane-keeping system had a much higher than average observed use rate in a prior IIHS study of vehicles at service centers.

The S90 avoided crossing the inside edge of solid lane markers by more than 35 centimeters on 100 percent of the trials, and the Malibu avoided doing so on 80 percent of the trials. In contrast, the Accord and Fusion avoided crossing lane markers by more than 35 centimeters in less than 20 percent of the trials.

"Intervention that comes sooner rather than later may allow for more subtle input that keeps the vehicle in its lane, and it may encourage drivers to leave lane departure prevention on once they have experienced the system," says Ian Reagan, a senior research scientist with IIHS and the study's lead author.

"Waiting too long to initiate steering input or failing to prevent lane drifts greater than 35 centimeters may be what is prompting some drivers to turn off the systems," he says.

Did the car depart the lane by more than 35 cm? Percentage of trial outcomes across all scenarios with a solid lane marker